key/value iteration support for template dom-repeat

[tam4s]

Currently it's very clumsy to iterate over JavaScript Objects:

http://stackoverflow.com/questions/30781500/how-can-i-iterate-over-a-js-objects-key-values-in-polymer-1-0

It should be as simple as

<template is="dom-repeat" items="[[myobj]]">
    <span>[[item.key]]</span>: <span>[[item.value]]</span>
</template>

[arodic]

@tam4s the solution from stack overflow will not observe the object changes so any change you make to the object after binding will not be reflected in dom-repeat.

The need for this feature has been expressed numerous times here, here, here and ultimately, the issue was moved here by @kevinpschaaf to be implemented in 1.0.

[kevinpschaaf]

Closing, as the feature request is covered by #1385 and will be tracked there.